Thermoplastic Materials Engineering Plastics

1. Thermoplastic MaterialsEngineering Plastics

2. Engineering Thermoplastics • Replace metallic parts • Strength and stiffness • Retention of properties over range of temperatures • Toughness to withstand incidental damage • Dimensional stability • Low creep • Low CTE • Withstand environmental factors (UV, O2, chemicals) • Shaped easily

3. Engineering Thermoplastics • Compared to commodity plastics • More expensive • The commodity resins are all lacking some critical property • Some Engineering Thermoplastics are formed through the condensation polymerization process

4. Polyamides or Nylons (PA)

5. ( )n [ ]a [ ]b [ ]a [ ]b Polyamides or Nylons (PA)

6. PA General Family Characteristics • Polarity • Crystallinity • Sharp meltpoint • Strength • Comparison of higher & lower nylon numbers

7. PA General Family Characteristics • Transparent (barely)—cook in bag (turkey) • Anti-friction—not like PTFE but good • Toughness—excellent • Fatigue resistance—excellent • Water absorption—a weakness (.2-2.5%—must be dried for injection molding) • Highly crystalline

8. Nylon 6,6 Hexamethylenediamine (6 carbons)

9. Nylon 6,6 Adipic Acid (6 carbons)

10. Nylon 6,6 Water Nylon 6,6

11. Nylon 6 Amine Group Acid Group

12. Water Nylon 6

13. Properties of Specific Nylon Types • Nylon 6,6 – General • Nylon 6 – Copycat • Nylon 6,10 – Less water absorption • Nylon 6,12 – Flexibility and less water • Nylon 2,2 – Strength

14. Processing Nylon • Injection molding • Shrinkage—crystallinity—.018 in/in • Dry it first • Extrusion • Low melt viscosity • Be careful of decomposition • Fibers • Drawing • Crystallization • Orientation

15. Nylon History • Nature of polymer bonding not understood • Carothers • Difunctional monomers • Polymers—1000 units long • Larger units—molecular still to eliminate water • Control of melting point and length • Many combinations of polyesters • Trying polyamides • Settling on 6,6 • Carothers death • 3 weeks after patents • Tremendous success • Name • Delawear, Wacra, Norun, Nuron, Nulon, Nilon, Nylon

16. Aramids

17. Aramids

18. Acetals or Polyoxymethylenes (POM)

19. ( )n Acetals or Polyoxymethylenes (POM)

20. Acetal General Family Characteristics • Mechanical—do not embrittle, good impact strength • Moisture—very little (shower heads) • Chemical resistance—very high, resists stains, sensitive to strong acids and bases • Weathering—fair • Thermal—200o F • Electrical—good • Machining—like cutting brass • Adhesion—epoxy glues

21. Processing Acetals • Do not heat above 440o F • Melt viscosity is not too dependant on temperature

22. Acetal Copolymer ( ( n

23. Thermoplastic Polyesters (PET/PBT)

24. Thermoplastic Polyesters (PET/PBT) ( )n

25. Thermoplastic Polyester General Family Characteristics • PET • Higher mechanical stiffness • Strength by orienting chains not by H-bonding • Get 50% crystallinity • forced by mechanical stretching • PBT • crystallizes rapidly • processes faster • lower overall properties

26. Processing PET • Shape it (film, tape, fiber, extrude, etc) • Amorphous structure • Reheat and stretch in strength direction(s) • Cool to below Tg

27. Specific TP Polyester Types • Dacron fiber—mix with cotton or wool-gives permanent creases • Kodel – photo film • Mylar—transparencies, tapes • PETG—glycol modified, amorphous, like PVC

28. Polycarbonate

29. ( )n Polycarbonate

30. History • Solvent resistance (DuPont) • GE-Lexan • Properties • Polar • Stiffness of backbone • Long repeat unit

31. Properties • Solvent sensitivity—poor but nice for joining • Clear—except for UV yellowing, slight crystallinity • Hard • Ductile—nailed, sawed, drawn, punched, sheared, drilled • Tough—helmets, light covers, windows, roadside signs, bullet proof shields • Dimensional stability—low creep • Electrical resistance—good but not fantastic • Machining—good

32. Acrylics (PAN, PMMA)

33. )n ( )n ( Acrylics (PAN, PMMA)

34. Properties • Color (transparency)—20 years w/ <10% change • Weathering—best • Mechanical properties—average except for impact (brittle) • Chemical—chlorinated solvents attack it, acetone gives it cracks • Electrical—good

35. Uses • Signs • Counter tops—Corian • Decorative pieces • Floor waxes • Paint, fingernail polishes • Contact lenses, glasses

36. Processing • Casting (sheets)—syrup • Injection molding—good • Thermoforming—ok but brittle • Machining—similar to wood

37. Flouropolymers (PTFE, FEP, PFA)

38. Flouropolymers (PTFE, FEP, PFA) ( )n )n (

39. History of Discovery • Chambers plant • Making Freon • Gas cylinder

40. Properties • Most are strengthened by the tight bond between the Fluorine and the Carbon atoms • Slippery (anti-stick surfaces) • Chemical inertness • High temperature melting • Non-flammable • High electrical resistance • Very dense—2.13-2.2 (high melt viscosity)

41. Uses • O-rings • Non-stick surfaces • Insulation-electrical • Lubricant • Coatings • Gears

42. Processing • Not processable by extrusion or injection molding • Sintering • Put in approx shape and heat–620o F • Similar to processing powdered metals • Fusion • Ram extrusion • Compaction • Rods and tubes • Calendaring • Very poor adhesion

43. High Performance Thermoplastics

44. PPO Properties • Thermal stability—excellent (650o F) • High HDT = 375o F • Good cold properties (-275o F) • Low water absorption • Low heat expansion • Good solvent resistance, but can be solvent welded

45. PPO uses • Used to replace stainless steel for surgical equipment • Replace thermosets • Pump housings • Valve components • Video terminal housings

46. Polyaryletherketones (PEEK, PEK, and Others)

47. Ether Linkage Ketone Linkage Polyaryletherketones (PEEK, PEK, and Others)

48. Polysulfones (PSU and PES)

49. Polysulfones (PSU and PES)

50. Properties • Resistant to oils • Heat stability (300o F) • Creep resistance • SO2 group adds stiffness • More dimensionally stable than PPO • Toughness—good